[USRP-users] Latency Through RF NoC on X310

Johnathan Rodgers john.rodgers102 at gmail.com
Tue Apr 21 09:35:59 EDT 2015


Hi,
Is there an alternative solution to measure the minimum loopback latency in
the fpga ?
I tried to do as follow (radio0 --> radio1) with RFnoc in grc without any
success : radio0 stays connected.
Thanks in advance.
Johnathan
 Le 19 mars 2015 23:28, "Martin Braun" <martin.braun at ettus.com> a écrit :

> FG == flow graph (what GRC produces).
>
> What I mean is a flow graph such as this: http://imgur.com/LuBHfxp
>
> However, we just yesterday realized that if you do this, the Rx radio
> won't be kicked off. We'll have a fix for that soon.
>
> Cheers,
> M
>
> On 19.03.2015 14:53, Johnathan Rodgers wrote:
>
>> Hi,
>> Martin, what do you mean by :
>> "To measure loopback latency, you'd need a simple GRC FG that connects
>> the rx radio to the tx directly on the FPGA".
>> Is it a simple radio0 --> radio1 connection in Gnuradio with a src/sink ?
>> What does FG mean ?
>> Thanks in advance.
>> Johnathan
>>
>> Nevermind again.
>>
>> On Wed, Mar 18, 2015 at 4:14 PM, John Malsbury
>> <jmalsbury.personal at gmail.com <mailto:jmalsbury.personal at gmail.com>>
>> wrote:
>>
>>     "Traceback (most recent call last):
>>        File "/home/jmalsbury/src/gr-ettus/build/top_block.py", line 122,
>>     in <module>
>>          tb = top_block()
>>        File "/home/jmalsbury/src/gr-ettus/build/top_block.py", line 63,
>>     in __init__
>>          self.device3,
>>        File
>>     "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/hier_block2.py",
>>     line 93, in __getattr__
>>          return getattr(self._impl, name)
>>     AttributeError: 'top_block_sptr' object has no attribute 'device3'"
>>
>>     Am I missing some device args?
>>
>>     On Wed, Mar 18, 2015 at 4:07 PM, John Malsbury
>>     <jmalsbury.personal at gmail.com <mailto:jmalsbury.personal at gmail.com>>
>>     wrote:
>>
>>         I'm blind.  disregard
>>
>>         On Wed, Mar 18, 2015 at 4:00 PM, John Malsbury
>>         <jmalsbury.personal at gmail.com
>>         <mailto:jmalsbury.personal at gmail.com>> wrote:
>>
>>             So... is there an RF NoC 101?  I've used the UHD src/sink in
>>             the UHD->RF NoC category.  is there anything I need to
>>             specify to route from Rx/Radio0 to RxRadio1?
>>
>>             -John
>>
>>
>>
>>             On Fri, Mar 13, 2015 at 2:21 PM, Martin Braun via USRP-users
>>             <usrp-users at lists.ettus.com
>>             <mailto:usrp-users at lists.ettus.com>> wrote:
>>
>>                 Yes, you can reduce the 'spp' value. It defaults to 364,
>>                 because that's what fits into a standard MTU.
>>
>>                 To measure loopback latency, you'd need a simple GRC FG
>>                 that connects the rx radio to the tx directly on the
>>                 FPGA, and a scope or something to see the delay. In GNU
>>                 Radio, give the rx radio a stream arg value 'spp=20' or
>>                 whatever. There may be limits to the size, and
>>                 non-multiples of 64-bits won't do you any good (2 sc16
>>                 samples per line).
>>
>>                 M
>>
>>
>>                 On 13.03.2015 11:32, John Malsbury via USRP-users wrote:
>>
>>                     Are there any UHD tricks I might use to stream the
>>                     output of a radio
>>                     block through RF NoC, directly to the other radio
>>                     block for re
>>                     transmission, without any FPGA mods?  I would like
>>                     to test/measure the
>>                     lowest delay possible across the rx frontend, ADCs,
>>                     RF NoC, DACs and tx
>>                     frontend...
>>
>>                     Are there knobs to tweak to reduce latency across RF
>>                     NoC (samples/frame
>>                     or equivalent)?
>>
>>                     -John
>>
>>
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